The overall objective of this research project remains the elucidation of fundamental principles underlying the vestibulo-ocular reflex function. Two main categories of studies are proposed. To investigate the anatomo-physiological correlates of sensory transduction in the labyrinth, primary afferent vestibular neurons will be studied with intracellular electrodes to determine their physiological properties and to inject dyes to visualize their morphological characteristics and areas of innervation in the cristae and CNS. Experiments will be conducted in frogs, chinchillas and rabbits. These Type II) and areas of innervation from the cristae (apex vs. slope, center vs. periphery) and relate them to the physiological response properties. To elucidate the significance of neural pathways and connections in the vestibulo-ocular reflex (VOR) and visual-vestibulo-ocular reflex (VVOR) arcs, eye movement responses to visual and/or vestibular stimulation will be obtained before and after experimental lesions in rabbits and primates. These will include: (1) bilateral flocculectomies, (2) complete cerebellectomies and, (3) coagulation of the fovea or the visual streak in primates and rabbits. Also measurements will be made of single neurons activity in the vestibular nuclei and adjoining reticular formation in normal and bilateral flocculectomized alert, non-anesthetized rabbits. Programs for on-line quantification of either compensatory or saccadic eye movements and neural activity will be used to expedite the evaluation of experimental results and accurately quantify changes in reflex function.